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I was tearing my hair out and about to give up for the night when I finally found your comment. 64-bit grid, same problem on 10.2.2. Thanks for posting this.
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10-05-2015
11:23 PM
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Thanks Curtis, I don't often deal with calculating areas through geoprecessing tools and didn't realize the data frame setting is inconsequential. I'd still be curious to know how ArcMap is calculating area values for GCS (unprojected) data with the Tabulate Intersection tool. Here's a comparison for one of my polygons: AreaKM2_Gdsic AreaKM2_MollW AreaKM2_PlateC AreaKM2_TabInt 907.4346 912.9755 935.2109 932.078 My comment about a "default" projection was simply in reference to whatever projection Esri uses to visualize a geographic coordinate system on my 2D computer screen. See definition 2 here.
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04-07-2015
10:43 AM
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Some follow up to my own question — looks like Tabulate Intersection does not respect the selected on-the-fly coordinate system. I recall reading somewhere that the defacto ArcMap display projection for unprojected (geographic) data is roughly equivalent to Plate Carree. Sure enough, with Plate Carree selected as my projection, calc geometry for the polygon gives an area value of 116.605551 km2 — that's pretty close to the original Tabulate Intersection value. And if I transform the projection of my zonal and class feature classes to Mollweide prior to running Tabulate Intersection, I end up with the expected area value: 96.866546 km2. Looks like you can't take shortcuts with Tabulate Intersection, needing to transform data to the appropriate projection before running the tool. Good to know where the apparent error was originating, but is this the intended behavior for this tool?
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03-31-2015
02:06 PM
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Hi all, I am trying to understand an issue with a relatively simple overlay analysis. I have two polygon feature classes: 1 for my zones (with 1 zone field), and 1 for my classes (no class fields). My global data are all WGS_1984, so I am projecting on-the-fly to get area calculations (Mollweide) in km2. When I run the "Tabulate Intersection" tool, I get what appear to be accurate percentage values, but very much inaccurate area values. As an easy illustration of the issue, see the example values below for a zone with 100% intersection: Tabulate Intersection PERCENT: 100% Tabulate Intersection AREA: 116.2149223 km2 Zone polygon area (from calculate geometry): 96.86654592 km2 Intersect tool area (from calculate geometry): 96.866546 km2 Any clue what is going on here? What am I not understanding about the Tabulate Intersection tool that leads to this discrepancy?
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03-31-2015
12:49 PM
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